X-ray imaging system use and calibration

Abstract

The present disclosure relates to determining the position of an X-ray focal spot in real time during an imaging process and using the focal spot position to ensure alignment of the focal spot and high-aspect detector elements or to correct for focal spot misalignment, thereby mitigating image artifacts. For example, the focal spot position may be monitored and may be adjusted in real-time using electromagnetic electron beam steering during a scan. Alternatively, previously determined functional relationships between focal spot position and measured data may be applied to address or correct for focal spot misalignment in the acquired data.

The invention claimed is: 
     
       1. A method for generating calibration data, comprising:
 emitting X-rays from a focal spot of an X-ray source at a plurality of focal spot positions in one or more spatial dimensions; 
 for each position, generating paired response data, wherein the paired response data comprises a first measurement from a first detector element of a sensor pair and a second measurement from a second detector element of the sensor pair, wherein the first detector element and the second detector element of the sensor pair have complementary response functions with respect to movement of the focal spot in the one or more dimensions, wherein the first detector element and the second detector element of the sensor pair are disposed adjacent to each other, and wherein the complementary response functions are symmetric about a perfectly aligned focal spot position so that the X-rays incident on one of the first detector element or the second detector element decreases as the X-rays incident on the other of the first detector element or the second detector element increases; and 
 associating at least the paired response data and corresponding positions in the one or more spatial dimensions to generate one or more functional relationships. 
 
     
     
       2. The method of  claim 1 , wherein the one or more spatial dimensions include a spatial dimension in a slice direction along a bore of a computed tomography (CT) scanner. 
     
     
       3. The method of  claim 1 , wherein the sensor pair comprises an attenuating layer positioned between the first detector element and the second detector element, wherein X-ray attenuation caused by the attenuating layer causes the complementary response functions of the first detector element and the second detector element with respect to position of the focal spot in the one or more spatial dimensions. 
     
     
       4. The method of  claim 3 , wherein the first detector element and the second detector element of the sensor pair comprise a low atomic number conversion material having a sufficient thickness in a spatial dimension corresponding to the direction of X-ray travel to discern a complementary response function. 
     
     
       5. The method of  claim 1 , wherein the one or more functional relationships further incorporate one or more operating conditions in addition to the paired response data and the corresponding positions in the one or more spatial dimensions. 
     
     
       6. The method of  claim 5 , wherein the one or more operating conditions comprise an operating voltage of the X-ray tube, a level of pile-up in the detector, an mA setting of the X-ray tube, or a combination of materials in the X-ray beam path for spectral calibration. 
     
     
       7. The method of  claim 1 , wherein the one or more functional relationships comprise one or more of response surfaces or look-up tables. 
     
     
       8. A method of addressing X-ray focal spot misalignment, comprising:
 emitting X-rays from an X-ray source comprising a focal spot, wherein the X-rays pass through an imaging volume in which a patient or object being scanned is positioned; 
 acquiring response data from one or more reference sensor pairs positioned where the X-rays incident on the reference sensor pairs do not pass through the patient or object, wherein the response data for each reference sensor pair comprises a first measurement from a first detector element of the respective sensor pair and a second measurement from a second detector element of the respective sensor or pair, wherein the first detector element and the second detector element of the each reference sensor pair have complementary response functions with respect to movement of the focal spot in one or more spatial dimensions, wherein the first detector element and the second detector element of each reference sensor pair are disposed adjacent to each other, and wherein the complementary response functions are symmetric about a perfectly aligned focal spot position so that the X-rays incident on one of the first detector element or the second detector element decreases as the X-rays incident on the other of the first detector element or the second detector element increases; 
 determining a position in the one or more spatial dimensions of the focal spot using the response data from the one or more reference sensor pairs; and 
 performing corrective action based on the position of the focal spot in the one or more spatial dimensions. 
 
     
     
       9. The method of  claim 8 , wherein the one or more spatial dimensions include a spatial dimension in a slice direction along a bore of a computed tomography (CT) scanner. 
     
     
       10. The method of  claim 8 , wherein the one or more reference sensor pairs each comprise an attenuating layer positioned between the first detector element and the second detector element of the respective reference sensor pair, wherein X-ray attenuation caused by the attenuating layer causes the complementary response between the first detector element and the second detector element with respect to position of the focal spot in one or more spatial dimensions. 
     
     
       11. The method of  claim 8 , further comprising acquiring additional response data from a plurality of active sensor pairs positioned where the incident X-rays on the active sensor pairs pass through the patient or object. 
     
     
       12. The method of  claim 11 , wherein performing corrective action comprises:
 based on the position in the one or more spatial dimensions of the focal spot, determining one or more corrective actions to perform on the additional response data based on one or more previously determined functional relationships, wherein the functional relationships are derived for different positions of the focal spot in the one or more spatial dimensions and one or more different operating conditions. 
 
     
     
       13. The method of  claim 12 , wherein the one or more functional relationships comprise one or more of response surfaces or look-up tables. 
     
     
       14. The method of  claim 12 , wherein the different operating conditions comprise one or more of an operating voltage of the X-ray tube, a level of pile-up in the detector, an mA setting of the X-ray tube, or a combination of materials in the X-ray beam path for spectral calibration. 
     
     
       15. The method of  claim 8 , wherein performing corrective action comprises adjusting the position of the focal spot to correct for deviation of the position of the focal spot. 
     
     
       16. An X-ray imaging system, comprising:
 an X-ray source configured to emit X-rays from a focal spot during operation; 
 a detector configured to generate signals corresponding to X-ray intensity when exposed to X-ray emission by the X-ray source, wherein the detector comprises a plurality of sensor pairs, each sensor pair comprising a first detector element and a second detector element separated by an attenuating layer and having complementary response functions with respect to position of the focal spot in one or more spatial dimensions, wherein the first detector element and the second detector element of each sensor pair are disposed adjacent to each other, and wherein the complementary response functions are symmetric about a perfectly aligned focal spot position so that the X-rays incident on one of the first detector element or the second detector element decreases as the X-rays incident on the other of the first detector element or the second detector element increases; 
 one or more processing circuits configured to:
 cause emission of X-rays from the X-ray source, wherein the X-rays pass through an imaging volume in which a patient or object being scanned is positioned during operation; 
 acquire response data from one or more reference sensor pairs of the plurality of sensor pairs, wherein the reference sensor pairs are positioned where the X-rays incident on the reference sensor pairs do not pass through the patient or object; 
 determine a position of the focal spot in the one or more spatial dimensions using the response data from the one or more reference sensor pairs; and 
 perform corrective action based on the position of the focal spot in the one or more spatial dimensions. 
 
 
     
     
       17. The X-ray imaging system of  claim 16 , wherein the X-ray imaging system comprises a computed tomography (CT) imaging system. 
     
     
       18. The X-ray imaging system of  claim 16 , wherein the one or more spatial dimensions include a dimension in a slice direction of the X-ray imaging system. 
     
     
       19. The X-ray imaging system of  claim 16 , wherein the first detector element and the second detector element of the sensor pairs comprise a low atomic number conversion material having a sufficient thickness in a spatial dimension corresponding to the direction of X-ray travel to discern a complementary response function. 
     
     
       20. The X-ray imaging system of  claim 16 , wherein the one or more processing circuits are further configured to acquire response data from one or more active sensor pairs of the plurality of sensor pairs, wherein the active sensor pairs are positioned where the X-rays incident on the active sensor pairs pass through the patient or object. 
     
     
       21. The X-ray imaging system of  claim 20 , wherein the one or more processing circuits are further configured to perform corrective action by determining one or more corrective actions to perform on the response data acquired by the active sensor pairs based on one or more previously determined functional relationships, wherein the functional relationships are derived for positions of the focal spot in the one or more spatial dimensions and one or more different operating conditions. 
     
     
       22. The X-ray imaging system of  claim 16 , wherein the one or more processing circuits are further configured to perform corrective action by adjusting the position of the focal spot to correct for deviation of the position of the focal spot.